1. Field of the Invention
The invention relates to a fuel cell separator, a manufacturing method thereof, and a fuel cell. More particularly, the invention relates to a fuel cell separator provided between adjacent single cells in a fuel cell having a plurality of single cells stacked on each other, for forming a fuel gas flow path or an oxidized gas flow path together with an adjacent member and for separating the fuel gas and the oxidized gas from each other, a manufacturing method thereof, and the fuel cell.
2. Description of Related Art
A fuel cell gas separator is a member that forms a fuel cell stack having a plurality of single cells stacked on each other. The fuel cell gas separator has sufficient gas non-permeability in order to prevent the fuel gas and oxidized gas supplied to each of adjacent single cells from mixing together. Conventionally, such a fuel cell gas separator has been manufactured by using a carbon material or metal material. In general, a metal material has a good strength, and therefore makes it possible to manufacture a thinner gas separator as compared to the case of the carbon material. Such a reduced thickness of the gas separator enables reduction in overall size of the fuel cell. Moreover, a metal gas separator can be manufactured by a simple method of pressing a metal sheet. As a result, a quick, simplified manufacturing process can be realized, resulting in improved productivity. Thus, increase in manufacturing cost can be prevented.
A metal used for manufacturing the metal gas separator can be selected as appropriate from the metals having sufficient electrical conductivity, strength and formability. In particular, by using a metal that is mass distributed as a metal material like stainless steel and aluminum, significant reduction in manufacturing cost can be achieved. The use of such a metal material normally requires the structure for ensuring sufficient corrosion resistance in the operation environment of the fuel cell. As the structure for improving corrosion resistance of the gas separator, the structure of coating the surface of the gas separator with silver has been proposed (e.g., Japanese Patent Laid-Open Publication No. SHO 60-115173). By coating the surface with silver, corrosion resistance of the metal gas separator can be significantly improved.
However, in the case where plating is used to coat the gas separator with a metal having excellent corrosion resistance, it is difficult to form a sufficiently compact coating layer. In other words, pores are formed in the coating layer. As a result, even if the coating layer itself is formed from a noble metal having excellent corrosion resistance, a substrate portion of the separator covered with the coating layer is gradually corroded through the pores formed therein, whereby the overall corrosion resistance of the gas separator is reduced. In order to sufficiently suppress the effects of corrosion through the pores in the coating layer, it is necessary to form the coating layer with a larger thickness, resulting in increase in the amount of the noble metal to be used. Therefore, the use of such a method is not desirable.